About driver rotation Degree and Radian
It's correct that the value is in radians. Blender uses radians for angles internally, since this is common practice for the calculation of trigonometric functions. The conversion to degree is only for display purposes in the user interface.

The same situation can be seen in the Python API. Assuming that you have an object named 'Cube' in your scene which is rotated 180° around the x-axis. When accessing the Euler rotation

bpy.data.objects["Cube"].rotation_euler.x


you will see that it returns 3.1415927410125732 which is a rough approximation of $\pi$.

This was previously asked on the bug tracker in T29797.